Molecular sieve materials, both natural and synthetic, have been demonstrated to have catalytic properties for various types of hydrocarbon conversion. Examples of molecular sieve materials include zeolites, SAPOs, AlPOs, and mesoporous materials. Typically molecular sieve materials are ordered, porous crystalline compositions having a definite crystalline structure as evidenced by their X-ray diffraction pattern. The pores in crystalline molecular sieve materials may vary in cross sectional dimensions from about 2 Å to about 1000 Å.
One particularly important class of molecular sieve materials are the aluminosilicate zeolites, which are described in “Atlas of Zeolite Framework Types”, eds. W. H. Meier, D. H. Olson and Ch. Baerlocher, Elsevier, Fifth Edition, 2001, which is hereby incorporated by reference. Such zeolites generally are generally described as microporous materials in that they have a pore size between about 2 and about 13 Å and are usually sub-divided into large, medium and small pore materials. A large pore zeolite generally has a pore size of at least about 7 Å and includes LTL, VFI, MAZ, FAU, OFF, BEA, and MOR framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of large pore zeolites include mazzite, offretite, zeolite L, VPI-5, zeolite Y, zeolite X, omega, and Beta. An intermediate pore size zeolite generally has a pore size from about 5 Å to less than about 7 Å and includes, for example, MFI, MEL, EUO, MTT, MFS, AEL, AFO, HEU, FER, MWW, and TON framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of intermediate pore size zeolites include ZSM-5, ZSM-11, ZSM-22, MCM-22, silicalite 1, and silicalite 2. A small pore size zeolite has a pore size from about 3 Å to less than about 5.0 Å and includes, for example, CHA, ERI, KFI, LEV, SOD, and LTA framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of small pore zeolites include ZK-4, ZSM-2, SAPO-34, SAPO-35, ZK-14, SAPO-42, ZK-21, ZK-22, ZK-5, ZK-20, zeolite A, chabazite, zeolite T, gmelinite, ALPO-17, and clinoptilolite.
In addition to the microporous zeolites, another class of molecular sieve materials of increasing importance is the mesoporous materials, which typically have a pore diameter within the range of from about 13 Angstroms to about 200 Angstroms. Among this broad class of molecular sieve materials, particular attention has been focused on a family of materials, the M41S materials, which are similar to zeolites in that they have pores of uniform, albeit in the mesoprous range. The M41S family of mesoporous molecular sieves is described in J. Amer. Chem. Soc., 1992, 114, 10834.
Synthetic molecular sieves are often prepared from aqueous reaction mixtures (synthesis mixtures) comprising sources of appropriate oxides. Organic directing agents (also referred to as structure directing agents or templates) may also be included in the synthesis mixture for the purpose of influencing the crystallization of a molecular sieve having the desired structure. The use of such directing agents is discussed in an article by Lok et al., entitled “The Role of Organic Molecules in Molecular Sieve Synthesis” appearing in Zeolites, Vol. 3, October, 1983, pp. 282-291.
After the components of the synthesis mixture are properly mixed with one another, the synthesis mixture is subjected to appropriate crystallization conditions, such as for example in an autoclave. Such conditions usually involve heating of the synthesis mixture to an elevated temperature possibly with stirring, and possibly under pressure. When crystallization of the synthesis mixture is complete, the crystalline product is recovered from the remainder of the synthesis mixture and especially the liquid contents thereof. Such recovery may involve filtering the crystals and washing the crystals to remove the mother liquor and other residual synthesis mixture components. The crystals are then normally dried and subjected to high temperature calcination, e.g., at 540° C., particularly to remove any organic directing agent which may otherwise block the pores of the molecular sieve.
Synthetic molecular sieves are expensive, in part, because their production can generate wastewater streams from crystallization and post-crystallization treatment that contain organic directing agents, e.g., surfactants, which are expensive to remediate. Thus, a need exists for a highly efficient process of manufacturing molecular sieves which reduces both the amount of water used and wastewater produced. This disclosure provides a process of manufacturing molecular sieves from forming mixtures of high solids content, using a reactor having a high intensity mixer. In some cases, the process does not require filtering the reaction mixture after crystallization or washing the molecular sieve product before calcinations. Accordingly, the process combines the advantages of reduced cost, shorter crystallization time and higher yield with the minimization of wastewater generated during the molecular sieve manufacture.
WO 2005/066068 discloses a continuous or semi-continuous process for the hydrothermal manufacture of a microporous or mesoporous composition comprising feeding solid and liquid reagents into a heated reactor zone at a temperature between 200° C. and 500° C. with a residence time less than 24 hours wherein said solid reagents have a weight percent between 45% and 98% of said reagents. In the Examples, the solid and liquid reagents are generally mixed in a mixing device and then transferred to a separate reactor for hydrothermal crystallization.
WO 2009/055215 teaches making M41S materials from mixtures having a high solids content (20% to 50 wt % solids) by a process that allows the M41S product to be recovered without a purification step (filtration and/or washing). Crystallization can be carried out under static or agitated conditions in a conventional autoclave. However, this document does not disclose or suggest the use of a reactor capable of high intensity mixing to carry out molecular sieve crystallization. Moreover, in the Examples, crystallization is conducted without stirring on reaction mixtures which are apparently prepared outside the autoclave.
U.S. Pat. No. 6,664,352 to Fredriksen teaches preparing metallocene catalysts by mixing catalyst and porous particulate support in a mechanically fluidized state with a catalyst material. The process uses a mixer having horizontal axis counter-rotating interlocking mixing paddles where paddles on different but preferably parallel rotational axes pass through a common mixing zone. The mixer can have a Froude number of from 1.05 to 2.2. No suggestion or disclosure is made for using this mixer in the crystallization of molecular sieves.
U.S. Pat. No. 6,521,585 to Yamashita et al. discloses the production of crystalline alkali metal silicate granules which are stably formulated in detergents. Temperature-controllable agitating mixers carry out mixing of the crystalline alkali metal silicate with detergent at a Froude number of 1 to 12 to control particle size distribution of granules. Mixers include horizontal, cylindrical blending vessels having agitating impellers on an agitating shaft.
Various mixers useful to mix slurries, pastes, and plastic bodies are described in “Principles of Ceramics Processing”, Second Edition, James S. Reed, John Wiley & Sons, Inc., 1995, pp. 347-354.